Windshield wiper having reduced friction characteristics

ABSTRACT

A wiper blade made of a compound having a methyl vinyl silicone polymer, a filler, and a friction-reducing additive is provided. The friction-reducing additive is present in an amount from between about 5 and 42 weight percent. The average particle size of the friction-reducing additive is preferably less than about 25 microns, thereby permitting extrusion of the compound into the shape of a wiper blade. Polytetrafluoroethylene is preferred as a friction-reducing additive, but other substances, such as boron nitride or graphite could be used.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/123,306, filed May 19, 2008, which is a continuation of U.S. patentapplication Ser. No. 11/358,525, filed Feb. 21, 2006, now U.S. Pat. No.7,373,687, which is a continuation of U.S. patent application Ser. No.10/313,346, filed Dec. 6, 2002, now U.S. Pat. No. 7,028,367, whichclaims the benefit of U.S. Provisional Application No. 60/337,928, filedDec. 6, 2001. All of the above-mentioned applications are herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to windshield wipers and in particularto windshield wipers having a silicon rubber wiper blade thatincorporates PTFE.

2. Description of Related Art

Rain, sleet, and snow have always presented a vision problem for thedriver of a moving vehicle. The windshield wiper blade has attempted tominimize the problem by clearing the windshield of the light obstructingmoisture and debris. Such blades are typically formed of rubber orrubber-like materials. Over the years, wiper blades have been modifiedin many ways in order to enhance wipe quality and therefore visibilityduring precipitation. In some instances, the configuration of the bladehas been changed to give a plurality of contact surfaces on the blade.Various modifications have been introduced to improve the consistencyand integrity of the wiping edge.

Wiper designers have developed silicone-rubber-based wiper blades withsome success. Silicone rubber is a superior material to natural rubberfor several reasons. Silicone rubber, i.e., high molecular weight,vulcanizable polydiorganosiloxane, is able to withstand wide temperaturevariation without an appreciable effect on its physical properties.Further, silicone rubber is virtually unaffected by ultravioletradiation, even over long periods of time. It is also resistant toozone, oil, salt, water and other road and automotive chemicals.

Silicone rubber as used for wiper compositions has had one significantdrawback: it has an unacceptably high coefficient of friction withrespect to glass. Some of the early silicone wiper blades exhibited sucha high coefficient of friction that the wiper blades could tear loosefrom the wiper frame when wiping the windshield. Less catastrophiceffects of this high coefficient of friction include an unacceptablyloud squeak or chatter as the wiper traverses the windshield, andunacceptably high loads on the windshield wiper motor. The siliconewiper blades produced today have improved significantly but wiperdesigners continually search for improved solutions that would reducethe friction between the wiper blade and the windshield.

Polytetrafluoroethylene (PTFE) has been used in conjunction with wiperblades in an attempt to decrease friction between the wiper blade andthe windshield. However, the wiper blades are typically coated with PTFEafter the blade is cured. Coating a cured blade with PTFE is less thandesirable because the PTFE will wear off over time, thereby reducing theimproved frictional characteristics of the wiper blade.

Japanese Patent Application No. Hei 5[1993]-117530, by Hiroshi Honma,(the “Honma Application”) describes compounding a fluoro resin powderfrom 0-10 parts by weight with a silicone rubber formulation for wiperblades. The application teaches that the formulation provides excellentclimate resistance and causes no vibration or squeaking. Fluoro resinpowder, such as PTFE, is added to the compound in a preferable amount of1-10 parts by weight, and an average particle size of 40 m. As describedin more detail below, the primary problem with compounding PTFE asdescribed in the Honma Application is that the particle size of the PTFEhinders the manufacturability of the compound. Larger particle sizes ofPTFE tend to increase the plasticity of the silicone rubber compounds,which reduces the ability to extrude the compound, and in some cases theability to mold the compound.

A need therefore exists for a windshield wiper blade made of a siliconerubber compound that provides excellent friction characteristics whenwiping a windshield. The reduced friction characteristics of the wiperblade will preferably allow a significant reduction in the forcerequired to move the wiper blade across the windshield and will reducethe amount of chatter, squeaking, jumping, and other noise inducing andperformance reducing actions associated with current wiper blades. Aneed further exists for a windshield wiper blade having these propertiesthat is simple and inexpensive to manufacture. Preferably, the materialsused in the wiper blade compound will be readily available andinexpensive. Finally, a need exists for a wiper blade compound that hasa relatively low plasticity, thereby allowing the compound to be easilyformed by a variety of manufacturing methods, including extrusion.

SUMMARY

The problems presented by existing wiper blades are solved by thesystems and methods described herein. A silicone wiper blade compoundaccording to one embodiment includes a methyl vinyl silicone polymer, afiller, and a friction-reducing additive. The methyl vinyl siliconepolymer may be provided in an amount from about 22 to 55 weight percent,the filler in an amount from about 35 to 50 weight percent, and thefriction-reducing additive in an amount from about 5 to 42 weightpercent. A preferred friction-reducing additive is PTFE having anaverage particle size of less than 6 μm and being compounded in anamount of about 11 weight percent. Alternatively, boron nitride,graphite, or other friction-reducing additives could be used.

In another embodiment, a windshield wiper includes a wiper blade of thecomposition described above. The wiper blade is attached to a framewhich is adapted for attachment to a vehicle.

A method for manufacturing a wiper blade according to another embodimentis further provided. The method includes compounding a mixture similarto that described above and forming the wiper blade from the mixture.The wiper blade may be formed by extrusion, molding, or any othermanufacturing process to create a wiper blade having any one of avariety of cross-sectional shapes.

Other objects, features, and advantages of the illustrative embodimentswill become apparent with reference to the drawings, detaileddescription, and claims that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a perspective view of a wiper blade according to anillustrative embodiment, the wiper blade being received by a splinemember, which is in turn connected to a wiper frame;

FIG. 2 depicts a perspective view of the wiper blade of FIG. 1;

FIG. 3 illustrates a cross-sectional front view of a wiper bladeaccording to an illustrative embodiment;

FIG. 4 depicts a cross-sectional front view of another embodiment of awiper blade;

FIG. 5 illustrates a cross-sectional front view of another embodiment ofa wiper blade;

FIG. 6 depicts a cross-sectional front view of another embodiment of awiper blade;

FIG. 7 illustrates a cross-sectional front view of another embodiment ofa wiper blade;

FIG. 8 depicts a side view of an extruder for manufacturing the wiperblade;

FIG. 9 illustrates a perspective view of a die used with the extruder ofFIG. 8;

FIG. 10 depicts a perspective view of a pair of wiper-sized segments ofcured silicone elastomer according to an illustrative embodiment;

FIG. 11 illustrates a perspective view of an alternative die used withthe extruder of FIG. 8; and

FIG. 12 depicts a perspective view of an elastomer being extrudedthrough the die of FIG. 11.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following detailed description of the preferred embodiments,reference is made to the accompanying drawings which form a part hereof,and in which is shown by way of illustration specific illustrativeembodiments in which the invention may be practiced. These embodimentsare described in sufficient detail to enable those skilled in the art topractice the invention, and it is understood that other embodiments maybe utilized and that logical mechanical, structural, and chemicalchanges may be made without departing from the spirit or scope of theinvention. To avoid detail not necessary to enable those skilled in theart to practice the invention, the description may omit certaininformation known to those skilled in the art. The following detaileddescription is, therefore, not to be taken in a limiting sense, and thescope of the present invention is defined only by the appended claims.

Referring to FIGS. 1 and 2 in the drawings, a windshield wiper 11according to an illustrative embodiment includes a wiper frame 13, aspline member 15, and a wiper blade 17. Wiper blade 17 includes a splinereceiving portion 21 and a squeegee member 23. Spline receiving portion21 includes a thin neck 25, and a relatively thick retainer flange 27integrally connected to the neck 25.

Squeegee member 23 varies in thickness between a thick base 31 and arelatively thin squeegee blade end 33. In a preferred embodiment, eachside 35 of the squeegee member 23 is inwardly arcuate from the base 31to the squeegee blade end 33. The squeegee member 23 is integrallyconnected to the neck 25 opposite retainer flange 27. The retainerflange 27, the neck 25, and the squeegee member 23 extend axially alonga longitudinal axis 37.

Referring still to FIG. 1 in the drawings, the spline receiving portion21 of wiper blade 17 is configured to receive spline member 15 along theaxial length of the wiper blade 17. Spline member 15 is engaged by aclaw 41 connected to wiper frame 13. Movement of wiper frame 13 relativeto a windshield 45, or other surface, causes the wiper blade 17 toremove moisture and other debris from the windshield 45.

Referring to FIGS. 3, 4, 5, 6, and 7 in the drawings, variouscross-sections of wiper blades are illustrated. Each wiper bladeincludes spline receiving portion 21, squeegee member 23, and blade end33.

Referring more specifically to FIG. 3, a wiper blade 46 includes aretainer flange 47 and a neck 49 defined by longitudinal grooves 51 oneither side of neck 49. The longitudinal grooves 51 extend the length ofwiper blade 46 on opposite sides of the neck 49. Dimensions A, B, C, D,E, F, G, and H as well as radii R₁ and R₂ are found in Table 1 below forthe wiper blade shown in FIG. 3. Dimensions B, C, D, and F are primarilydetermined according to the structure of the vehicle wiper frame 13 andspline 15. Dimensions A, G, H, R₁, R₂, hR₁, and wR₁ are chosen to giveoptimum design and wipe quality, and may vary according to the wiperblade composition. For example, length dimensions G and H would be maderelatively longer for stiffer compositions, or for compositions havingpolydiorganosiloxanes with a larger proportion of vinyl side groups inthem or having larger amounts of small-sized particulate fillers. Theend thickness A will also vary, as will the thickness E of the base 31,according to the relative resiliency of the cured composition.

TABLE 1 Dimension, in. Blade Profile A B C D E F G H FIG. 3 .035 .034.180 .045 .210 .140 .079 .231 FIG. 4 .038 .035 .110 .040 .230 .100 .070.275 FIG. 5 .035 .040 .220 .050 .230 .195 .060 .230 Blade Profile R₁ hR₁wR₁ R₂ FIG. 3 .236 .420 .229 .100 FIG. 4 .246 .364 .261 N/A FIG. 5 .125.377 .142 N/A

Referring now to FIG. 4 in the drawings, a wiper blade 52 includes aretainer flange 53 that is substantially more narrow than the retainerflange 47 illustrated in FIG. 3. A top wall 55 of wiper blade 52downwardly slopes from a sidewall 57 to a neck 58, instead of being atright angles to neck 58 and sidewall 57. Dimensions A through H, R₁,hR₁, and wR₁ are listed in Table 1 for the wiper blade 52.

A wiper blade 61 having a slightly different cross-section isillustrated in FIG. 5. The preferred dimensions for wiper blade 61 arelisted in Table 1. Wiper blade 61 includes a first neck 63 and a secondneck 65 of approximately the same dimension. A first retainer flange 66is disposed between first neck 63 and second neck 65, and a secondretainer flange 67 is integrally connected to second neck 65. Secondretainer flange 67 has beveled corners 69. The length of the second neck65 between first retainer flange 66 and second retainer flange 67 ispreferably about 0.045 inches. The thickness of the second retainerflange 67 is preferably about 0.055 inches while the thickness of theunbeveled top portion of the second retainer flange 67 is approximatelythe same dimension as the thicknesses of first neck 63 and second neck65.

Referring to FIG. 6 in the drawings, a cross-section of wiper blade 75is illustrated. Wiper blade 75 is adapted to be received by a wiperblade holder 76. The wiper blade 75 includes five integral ribs 77, 79,81, 83, and 85 which extend the length of the blade 75 and projectgenerally radially relative to a longitudinal axis of an upper tubularbody portion 93. The central rib 81 is a squeegee rib, and the ribs 77,79 and 83, 85 on opposite sides of the squeegee rib 81 are scrapingribs. The squeegee rib 81 is slightly longer than the scraping ribs 77,79, 83, and 85.

The dimensional relationships between an upper tubular body portion 93,a neck 95, a lower tubular body portion 97, and ribs 77-85 are importantto the proper function of wiper blade 75. The preferred dimensions ofthe wiper blade are illustrated in Table 2. It should be noted that theangle between the ribs 77, 79, 81, 83, and 85 is approximately 30E andthe included angle of the points on the ribs 77, 79, 83, and 85 isapproximately 4E. It should also be noted that the squeegee rib 81 has aconcave end face 99 at blade end 33 in order to present a relativelysharp edge to the surface being wiped.

TABLE 2 Dimension, in. Blade Profile A B C D E F G FIG. 6 .300-.315.210-.225 .160 .165 .250 .350 .095

Referring to FIG. 7 in the drawings, a cross-sectional view of a wiperblade 107 is illustrated. The spline-receiving portion 21 includes anupper surface 115 having an entry slot 117. A spline channel 119 isdisposed within spline-receiving portion 21 and is adjacent to andcommunicable with entry slot 117. Preferably, both entry slot 117 andspline channel 119 extend the entire length of wiper blade 107 parallelto a longitudinal axis of spline-receiving portion 21. In a preferredembodiment, entry slot 117 is not as wide as spline channel 119, and aretention shoulder 125 is disposed on each side of entry slot 117.Retention shoulders 125 are flexible, and are therefore configured tobend away from entry slot 117 such that a single-rail spline (not shown)can be inserted into spline channel 119. After the single-rail spline isseated within spline channel 119, both retention shoulders 125 reboundto secure the spline within the spline channel 119.

Spline-receiving portion 21 also includes two frame attachment grooves131 that extend the length of wiper blade 107. Frame attachment grooves131 are configured to slidingly receive claws similar to claw 41 (seeFIG. 1). Protrusions on the claws fit into grooves 131. Although theclaws used with some wiper frames are crimped around the wiper blade,with wiper blade 107 it is preferred not to crimp the claws, but insteadto allow the wiper blade 107 to slide within the protrusions. Whenslidingly received by the claws, the wiper blade 107 is further securedwith a pair of end caps (not shown). One end cap is installed on eachend of wiper blade 107 to prevent wiper blade 107 from sliding out ofthe grasp of the claws.

A person having skill in the art will recognize that the presence ofretention shoulder 125 is not absolutely necessary and that in such ascenario, entry slot 117 would be at least as wide as spline channel119, and the single-rail spline would most likely be secured by afriction fit between the spline and the walls of the spline channel 119.It is also conceivable that only one retention shoulder 125 is providedthat extends from one side of spline-receiving portion 21 and eitherpartially or completely covers the single-rail spline. It is furtherpossible that entry slot 117 be disposed on a surface ofspline-receiving portion 21 other than top surface 115. For example, theentry slot 117 could be located on a side surface of spline-receivingportion 21, as long as the entry slot 117 is still communicable with andadjacent to spline channel 119. Finally, in some embodiments, a wiperblade having a single-rail spline similar to wiper blade 107 could beprovided without an entry slot 117. In that embodiment, the single-railspline would be co-extruded or co-molded with the wiper blade so thatthe single-rail spline was permanently disposed within the splinechannel 119.

The wiper blades described herein (including wiper blades 17, 52, 61,75, and 107) are constructed from a silicone rubber formulation thatincorporates PTFE powder or another friction-reducing additive directlyinto the compound. The preferred composition of the silicone rubberformulation of the present invention is shown in Table 3.

TABLE 3 Material Weight % Methyl Vinyl Silicone Polymer  22-5% Filler(Silica, Ca, or other mineral)   35-50% Friction-reducing additive(PTFE, Graphite, Boron Nitride, or   5-42% other additive) OH endedSilicone Polymer   1-15% Cerium Stabilizer 0.1-1% Acid Acceptor 0.1-1%Pigment 0.1-1% Peroxide 0.5-2%

As illustrated in Table 3, the friction-reducing additive could includePTFE, graphite, boron nitride, fluoro-polymers, or otherfluorine-containing additives. When PTFE is used, a powder form of thecompound is added during the compounding stage of the silicone rubbermaterial, which is performed in a Banbury mixer. While a preferred rangefor the PTFE is between about 5 and 42 weight percent, it has been foundthat an optimum amount of PTFE is about 11 weight percent. Thepercentage of PTFE used in the compound, coupled with the averageparticle size of the PTFE, plays an important part in both the frictionreducing properties of the wiper blade and the ability to easilymanufacture the wiper blade. The average particle size of the PTFE couldbe as high as about 25 μm, but it is preferred that the average particlesize be below about 6 μm.

An example of PTFE commonly used in preparing the wiper blade compoundof the present invention is Polymist F-5A, which can be obtained fromAusimont USA. Polymist F-5A contains particles of a relatively smallsize, typically below 6 μm. Table 4 illustrates physical properties forPolymist F-5A.

TABLE 4 Average Particle Size, μm <6 Specific Surface Area, m²/g 3Specific Gravity at 23EC 2.28

It should be understood that the correct selection of amount andparticle size for the PTFE or other friction-reducing agent is based onthe benefit in reduced friction characteristics and the ability toeasily manufacture the resulting compound. Although certain amounts ofPTFE may provide better friction-reducing qualities to the compound, theplasticity of the resulting compound is sometimes increased to an extentthat extrusion and molding of the compound is difficult or impossible.Extrusion of wiper blades is often preferred over molding because theextrusion process is generally quicker and less expensive.

Several tests were conducted using various friction-reducing additivesto determine the effect the additives have on the frictioncharacteristics of the final compound. The testing protocol is arelatively standard test in the wiper industry for testing frictioncoefficients. A sample of test material is placed on a slab of glass,and a 200 g weight is applied to the test material. The amount of forcerequired to pull the material across the glass (the “pulling force”) isthen measured and recorded. A coefficient of friction is then calculatedby dividing the pulling force by the 200 g weight. Each material wastested five times, and an average pulling force was calculated.

Table 5 illustrates the test results for natural rubber and StandardJ-7721-1 TRPL, materials commonly used in windshield wiper blades, thelatter being used in wiper blades manufactured by JAMAK Fabrication,Inc. The test results illustrated in Table 6 are for silicone compoundsthat incorporate the listed friction-reducing additive. Thefriction-reducing additives listed in Table 6 are not intended torepresent an exhaustive list of additives that could be used in thecompound of the present invention. Instead, these additives are merelyexamples of some friction-reducing additives, and the values measuredduring testing give an indication of the friction-reducing qualitiesthat each additive provides.

TABLE 5 Calculated Coefficient Material Pulling Force (g) of FrictionNatural Rubber 598.7 2.99 Standard J-7721-1 TRPL 479.4 2.40

TABLE 6 Amount of Pulling Calculated Additive Force CoefficientFriction-reducing additive (pph) (g) of Friction ALGOFLON 203 11 221.11.11 CTF5 Boron Nitride 18 140.3 0.70 CTUF Boron Nitride 18 99.8 0.50R-020G Graphite 18 131.9 0.66 R-182B Graphite 18 127.0 0.64 Polymist F5A6 224.8 1.12 Polymist F5A 9 242.6 1.21 Polymist F5A 11 187.1 0.94Polymist F5A 12 274.2 1.37 Polymist F5A 15 290.3 1.45 Polymist F5A 16186.8 0.93 Polymist F5A 18 264.9 1.32 Polymist F5A 100 192.0 0.96Polymist F510 6 308.5 1.54 Polymist F510 9 253.6 1.27 Polymist F510 11169.5 0.85 Polymist F510 12 268.9 1.34 Polymist F510 15 245.7 1.23Polymist F510 18 246.4 1.23 Polymist XPA213 9 269.2 1.35 Polymist XPA2136 276.1 1.38 Polymist XPA213 11 127.2 0.64 Polymist XPA213 12 258.1 1.29Polymist XPA213 15 224.7 1.12 Polymist XPA213 18 216.1 1.08 Polymist F5A& F510 (2.75 & 8.25 11 141.3 0.71 pph) Polymist F5A & F510 (5.5 & 5.5 11147.3 0.74 pph) Polymist F5A & F510 (8.25 & 2.75 11 153.5 0.77 pph)Polyurethane 10 204.5 1.02 Silane Silwet L7607 0.2 304.2 1.52 SilaneSilwet L7608 0.2 295.6 1.48 Silane Silwet L77 0.2 422.6 2.11

As illustrated in Table 6, the type and amount of friction-reducingadditive used with the silicone compounds described herein significantlyaffects the frictional properties of the compound. As mentionedpreviously, the preferred silicone composition includes a PTFE additiveof Polymist F5A at 11 weight percent. The small average particle size ofthis friction-reducing additive reduces the coefficient of friction byapproximately 61 percent relative to a typical silicone wipercomposition such as Standard J-7721-1 TRPL. Although some of thematerials listed above exhibit even better frictional characteristicsthan Polymist F5A, the issue becomes one of cost and ease ofmanufacture. For example, the Polymist F5A at 16 weight percent providesslightly better frictional properties, but the increased cost of theadditional PTFE is not worth the small gain. A larger gain is obtainedby using Boron Nitride or Graphite, but the cost of these materials ismuch greater than Polymist F5A. Finally, some of the Polymist F510compounds, or blended compounds containing Polymist F510 and PolymistF5A, exhibit excellent friction characteristics, but the addition ofPolymist F510 sometimes makes the final silicone compound more difficultto extrude.

The Polymist F5A additive provides exceptional manufacturingcharacteristics to the silicone compounds described herein. Although allof the friction-reducing additives of Table 6 could be used to improvethe compound's friction characteristics over standard silicone wiperblade compounds, certain materials exhibit lower plasticity than others.Plasticity is a material property determined when a material sample issubjected to a yield force that causes the material to undergo apermanent change in shape or size (i.e. a plastic deformation). Themeasured plasticity values for the silicone compound incorporatingdifferent friction-reducing additives is illustrated in Table 7.

TABLE 7 Average Particle Size Test Loading Plasticity PTFE Additive (μm)(pph) (mm/100) Polymist F5A <6 11 250 Polymist F510 <20 11 718 Algoflon203 <6 11 258 Teflon 6C 480 4 560

The plasticity values listed in Table 7 were measured according to ASTMD531-00 Standard Test Method for Rubber Property-Pusey and JonesIndentation. It is preferable that a plasticity below 400 (mm/100) beused since values above 400 make extrusion, and even molding, of thecompound more difficult. The low plasticity associated with Polymist F5Amakes it one of the preferred choices as a friction-reducing additive.

In one embodiment, the wiper blades described herein may be manufacturedby extrusion. Referring to FIG. 8 in the drawings, the first step in themanufacturing process is to extrude a continuous length of curablesilicone compound 211 through an extruder 213.

Extruder 213 is a conventional extruder having a hopper 215 which feedsinto a hot cylinder. The heat softens the elastomer, and it is forced byone or more spiral screws (not shown) through a die 217 having a dieorifice. The die orifice forms a continuous mass of elastomer in theshape of one of the wiper cross sections previously described (see FIGS.3-7). Extrusion processes of this type are well known in the art.

Referring to FIGS. 9 and 10 in the drawings, a detailed view of die 217includes a die opening 219 which is shaped to produce a pair of wiperblades joined at a mid-section thereof in edge-to-edge relation. The die217 includes an adjustable scoring mechanism, such as adjustable blades227, 229. Blade tips 231 disposed on each adjustable blade 227, 279 arenot in contact, but are spaced apart a preselected distance to score thecontinuous length of elastomer 211 along a top and bottom surface 233,235 of the wiper blade to a depth less than the thickness of theelastomer (see FIG. 10). The blades 227, 229 can be adjusted by means ofscrews 237, 239 mounted on the die which are carried in vertical slotsprovided in the blades 227, 229.

The continuous length of extruded elastomer 211 is passed to a curingstation 241. In the embodiment shown in FIG. 8, curing station 241 is acontinuous vulcanizer. It is readily understood by those skilled in theart that the continuous vulcanizer 241 can employ, for instance, aliquid medium such as a eutectic salt bath having liquid salt at atemperature from about 350E to 450E F. The viscosity of the salt atthese operating temperatures is similar to water.

It will also be apparent that instead of the preferred salt bath, anycontinuous vulcanizing method could be used. For example, thevulcanizing step could easily be performed by a hot air vulcanizingtunnel. Also, the continuous length of elastomer 211 could be curedwithout a heat activated catalyst, instead using infrared radiation orgamma radiation techniques familiar to those skilled in the art. It isonly necessary that the previously formed and scored curable elastomerbe cured such that the material can be divided and formed assubsequently described.

After curing, a continuous length of cured elastomer 259 is separatedinto two separate lengths of wiper blade 243, 245 by allowing one length243 to travel over a fixed nip roller 247 while the second length 245 ispulled under the same nip roller 247. The beginning separation can beaccomplished by hand with the ends of the wiper blade being engaged byroller pairs 253, 255 of a puller 257. Preferably, the separation ofcured elastomer 259 occurs at an elevated temperature above ambient.Leaving the extruder 213, the curable elastomer 211 is typically at atemperature in the range from about 90°-100° F. The continuousvulcanizing step then typically raises the temperature to a higherelevation above ambient. For instance, in the case of a salt bath or hotair vulcanizing tunnel, the cured elastomer 259 would be at an elevatedtemperature on the order of 300°-450° F. The preferred temperature forthe cured elastomer 259 at the separating roller 247 is in the rangefrom about 100°-300° F., most preferably about 200° F. The decrease intemperature between the continuous vulcanizer 241 and the separatingroller 247 can be achieved by exposure to the ambient atmosphere, or bypulling cured elastomer 259 through a water trough with water at ambienttemperature, or by exposing cured elastomer 259 to a plurality of airjets.

Referring still to FIGS. 9 and 10, the separate continuous lengths ofwiper blade 243, 245 are cut transversely into individual wiper-sizedsegments 261, 263 by a conventional cutter 265. FIG. 10 is a perspectiveview of a pair of wiper-sized segments 261, 263, the segments beingseparated by an opening 267 located at the approximate mid-section whichformerly represented the score line prior to separation at the niproller 247.

Referring to FIG. 11 in the drawings, another embodiment of an extrusiondie 287 is illustrated. Die 287 includes blades 289, 291, the blade tips293 of which are not in contact but are spaced apart a preselecteddistance. In this case, however, a preforming means, such as wire 295,extends between the blades 289, 291 to preform a mid-section 298 of anextruded elastomer 297 by weakening the mid-section. The blades 289, 291are fixed on the die face by means of screw sets 299, 301, with wire 295being, for instance, tack welded thereon. The preforming means couldalso comprise, for instance, a Kevlar blade arranged between the dieblades 289, 291. By passing the raw extruded elastomer through die 287and preforming means 295, the elastomer reunites, or tacks together,immediately after passing the wire 295. The continuous length ofuncured, extruded elastomer 297 is then passed to a curing station andcured in the manner previously discussed.

After curing, a continuous length of cured elastomer is separated intotwo separate lengths of wiper blade (similar to lengths 243, 245 in FIG.8) by allowing one length of wiper blade to travel over a fixed niproller 247 while a second length of wiper blade is pulled under the sameroller 247. The lengths can then be engaged by roller pairs 253, 255 ofa puller 257, as previously discussed. The cured elastomer separatesalong the preformed mid-section 298 into separate lengths of wiper bladehaving improved edge quality. The extrusion process allows a continuouslength of blade to be formed at a lower cost than most moldingtechniques.

The fabrication process described in conjunction with FIGS. 11 and 12 isuseful for wiper blades having a specific gravity of less than or equalto about 1.40. For blade compositions having a specific gravity ofgreater than 1.40 the extrusion process is modified such that no Kevlarwire or filament 295 is used to preform a weakened midsection. Instead,the blades are extruded and are passed directly to the continuousvulcanizer 241 (see FIG. 8). Thereafter, the blades are separated not bythe nip rollers as shown, but by a circular blade. After separation, theblades are cut transversely by a conventional cutter 265.

The silicone rubber compositions described herein are ideally suited forextrusion into wiper blades of many different cross sections. Althoughthe extrusion process has been described in detail with reference toFIGS. 8-12, it will be understood by those of skill in the art that anyextrusion process could be used to form the wiper blades. It will befurther understood that other manufacturing processes, including withoutlimitation compression molding, injection molding, and blow molding,could be employed to form the wiper blades.

One advantage of the silicone composition and wiper blade of theillustrative embodiments described herein is the superior frictionproperties imparted to the wiper blade. The reduced friction betweenwiper blade and wiped surface reduces chatter on the wiped surfaceduring use and improves performance of the wiper blade. The compositionalso greatly reduces wiper edge wear and improves tear resistanceproperties, which increases the overall life of the wiper blade. Inaddition to these exceptional properties, the silicone rubberformulation retains the desirable properties often associated withsilicone, namely resistance to UV, ozone, and extreme temperatures.

Another advantage of incorporating PTFE or other friction-reducingadditives during the compounding stage is that the compound “blooms” ormigrates to the surface of the wiper blade and continues to providereduced friction characteristics over time. This is an improvement overwiper blades that have been coated with PTFE, since PTFE coatings tendto erode over time, thereby adversely affecting the wiper blade'sfrictional characteristics.

A person having ordinary skill in the art will recognize that variousforms and grades of PTFE could be added during the compounding stage,including PTFE in non-powder form and grades other than the PolymistF-5A described above. Alternative friction-reducing agents could also beused, including without limitation boron nitride and graphite.

Even though many of the examples discussed herein are applications ofthe illustrative embodiments in windshield wiper blades, the compoundsand techniques also can be applied to other devices that need a flexiblematerial having superior tear resistance and reduced frictioncharacteristics. Some examples of possible further uses include but arenot limited to squeegees for cleaning windows, medical tubing such asperistaltic pump tubing, and materials for various sealing applications.

It should be apparent from the foregoing that an invention havingsignificant advantages has been provided. While the invention is shownin only a few of its forms, it is not just limited but is susceptible tovarious changes and modifications without departing from the spiritthereof.

1. A windshield wiper comprising: a frame adapted to be attached to avehicle; a wiper blade attached to the frame; and wherein the wiperblade is made from a mixture including a methyl vinyl silicone polymerfrom about 22 to 55 weight percent, a filler from about 35 to 50 weightpercent, and polytetrafluoroethylene in an amount of from about 5 to 42weight percent, the polytetrafluoroethylene having an average particlesize of less than about 25 μm.